A common operation in integrated circuit fabrication is the deposition of a layer of crystalline material having a first lattice constant on a substrate consisting of a layer of material having a second lattice constant. If the first and second lattice constants differ significantly, the deposited layer contains dislocations resulting from the mismatch in the lattice constants. Such dislocations degrade the performance of the devices in which they appear. In addition, these dislocations can lead to further dislocations in subsequently deposited layers.
For example, GaN layers are particularly useful in constructing lasers in the blue and green wavelengths. These layers are typically deposited on a sapphire substrate. The lattice constants of GaN and sapphire differ by 13%. As a result, the GaN layer can have as many as 10.sup.9 dislocations per cm.sup.2.
Broadly, it is the object of the present invention to provide an improved method for depositing a layer of crystalline material on a crystalline substrate having a substantially different lattice constant from that of the deposited layer.
It is a further object of the present invention to provide a method for depositing GaN on sapphire which results in fewer dislocations in the GaN layer than obtained with conventional deposition techniques.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.